1. Field of the Invention
This invention relates to fuel cell stacks which utilize a metal hydroxide electrolyte and more particularly to means for preventing a carbonate buildup in the cells thereof.
2. Description of the Prior Art
Cells of one type of a fuel cell stack are comprised of an electrolyte and porous electrodes. Hydrogen and oxygen are provided at the respective electrodes thereby causing a resulting fuel cell reaction which furnishes an electrical output to a load. The source of the oxygen may be ambient air which contains between 500-1000 parts per million of carbon dioxide (CO.sub.2). The electrolyte is often an aqueous solution of an alkali metal hydroxide, such as potassium hydroxide (KOH). If CO.sub.2 enters the cell, it reacts with the electrolyte to form an alkali metal carbonate. The carbonate typically causes a voltage loss. High carbonate ion concentration may also result in the formation of a precipitate which accumulates at the surfaces of the porous electrodes of cells, thereby reducing the efficiency and performance thereof.
In U.S. Pat. Nos. 3,511,712 and 3,519,488, Giner discloses a means for removing the carbonate ions from the electrolyte of a fuel cell, whereby the electrolyte is regenerated. Giner establishes a hydroxyl ion gradient between electrodes of a fuel cell, thereby causing a conversion of the carbonate ions to CO.sub.2 and hydroxyl ions. Giner, however, requires the use of substantially pure hydrogen for obtaining the hydroxyl ion gradient. Additionally, a plurality of cells of the type disclosed by Giner may not, in some instances, be preferred in a fuel cell stack because a large hydroxyl ion gradient in each cell causes a large reduction of the voltage provided by the stack. Giner does not disclose how a single regenerator cell can be integrated with other cells of a fuel cell stack for regenerating the electrolyte of the entire stack.
Heretofore, an efficient, economical apparatus for regenerating the electrolyte of a fuel cell stack has been unknown in the prior art.